Direct writing of metallic structures for metamaterial applications

Ultrafast-laser micromachining allows for 3D fabrication of structures much smaller than the diffraction limited laser spot size in transparent media such as glass. Under a linear regime, the media does not absorb light at the operating wavelength of the laser. However, using ultrafast pulses, we can obtain material modification through non-linear absorption. The technique can also be used to induce chemical reactions. High intensity femtosecond laser pulses can induce the photoreduction of metal ions through non-linear absorption. We use solutions containing metal salts to grow metal structures using femtosecond lasers. The non-linear nature of the process allows us to limit absorption to volumes that are smaller than the diffraction limited spot size of our laser. Our goal is to push the resolution of the fabricated structures to 100 nm and beyond while minimizing surface roughness over large volumes.

The anticipated outcome is a nanofabrication technique that can be used to reliably pattern nanostructures in three dimensions and in bulk. A resolution of 100 nm would allow us to fabricate metamaterials for the long end of the optical spectrum, the near-infrared, and beyond. The method can be used for prototyping because arbitrary structures, as long as they are self-supporting or in a solid matrix, can be created through computer control. Femtosecond-laser fabrication offers an avenue for patterning metal nanostructures on a larger scale than currently possible. It could be used for many applications beyond metamaterials, including optoelectronics, electronics and biology due to its flexibility.